Removable pressure-sensitive adhesive strip

ABSTRACT

The invention relates to a pressure-sensitive adhesive strip, for the residue-free and nondestructive removal by which by substantially expanding it in the plane of adhesion, comprising an adhesive compound layer, said adhesive compound layer consisting of a pressure-sensitive adhesive compound, constituted by vinyl aromatic block copolymers and adhesive resins, at least 75 wt.-% (relative to the total amount of resin) of a resin being selected that has a DACP (diacetone alcohol cloud point) of greater than −20° C., preferably greater than 0° C., and a softening point (ring &amp; ball) of greater than or equal to 70° C., preferably greater than or equal to 100° C., and the pressure-sensitive adhesive compound being foamed.

This application is a 371 of PCT/EP2016/056785, filed Mar. 29, 2016,which claims foreign priority benefit under 35 U.S.C. § 119 of theEuropean Patent Application No. 15162318.8 filed Apr. 2, 2015, thedisclosures of which are incorporated herein by reference.

The invention relates to a pressure-sensitive adhesive strip based onvinyl block copolymers, which is of high tensile strength and can beused to produce a bond which can be parted again by extensive stretchingin the direction of the bond plane.

Self-adhesive tapes which have high elastic or plastic extensibility andwhich can be redetached without residue or destruction by extensivestretching within the bond plane are known from, for example, U.S. Pat.No. 4,024,312 A, DE 33 31 016 C2, WO 92/11332 A1, WO 92/11333 A1, DE 4222 849 C1, WO 95/06691 A1, DE 195 31 696 A1, DE 196 49 727 A1, DE 196 49728 A1, DE 196 49 729 A1, DE 197 08 364 A1, DE 197 20 145 A1, DE 198 20858 A1, WO 99/37729 A1 and DE 100 03 318 A1 and are also referred tobelow as strippable self-adhesive tapes.

These strippable self-adhesive tapes are oftentimes used in the form ofadhesive film strips which are pressure-sensitive on one or both sides,preferably having a non-adhesive grip region from which the detachmentoperation is initiated. Particular applications of such self-adhesivetapes are found in publications including DE 42 33 872 C1, DE 195 11 288C1, U.S. Pat. No. 5,507,464 B1, U.S. Pat. No. 5,672,402 B1 and WO94/21157 A1. Specific embodiments are also described in DE 44 28 587 C1,DE 44 31 914 C1, WO 97/07172 A1, WO 98/03601 A1 and DE 196 49 636 A1, DE197 23 177 A1, DE 197 23 198 A1, DE 197 56 084 C1, DE 197 56 816 A1, DE198 42 864 A1, DE 198 42 865 A1, WO 99/31193 A1, WO 99/37729 A1, WO99/63018 A1, WO 00/12644 A1 and DE 199 38 693 A1.

Preferred fields of use of aforementioned strippable adhesive-filmstrips include in particular the residuelessly and nondestructivelyredetachable fixing of light-weight and medium-weight articles in theresidential, work, and office segments. For use in the work and officesegments, the products used are generally of considerable thickness, ofmore than 400 μm.

In the consumer electronics industry—such as, for example, in theproduction of mobile telephones, digital cameras or laptops—there is anever-growing desire for a possibility of separating the individualcomponents on disposal after they have been used. Some components canthen be reused or recycled. Or at least separate disposal is possible.There is therefore great interest within this industry in redetachableadhesive bonds. In particular, adhesive tapes which can be easilyremoved as and when desired, while possessing a high holdingperformance, constitute a reasonable alternative here to adhesive stripswhich must first be pretreated, by heating, for example, in order to bedetached.

Within the consumer electronics segment, the preference is for adhesivestrips which are extremely thin, since the end devices are extremelythin and hence all of the individual components are to take up littlespace as well.

When very thin strippable adhesive strips are used which operate withoutcarriers, there is increased incidence of tears (see DE 33 31 016 C2).If the adhesive strips tear, then detachment is generally no longerpossible, however, since the remnant of the adhesive strip springs backinto the joint and there is therefore no grip tab available.

WO 92/11333 A1 describes a strippable adhesive tape which uses as itscarrier a highly stretchable film with a resilience after stretching of<50%.

WO 92/11332 A1 describes an adhesive film strip which is redetachable bypulling in the bond plane and for which the carrier utilized may be ahighly stretchable, substantially nonresilient film. Adhesives employedare exclusively UV-crosslinked acrylate copolymers, with which it is notpossible to achieve the high bond strengths, and which undergo a smallerloss of peel adhesion during stretching than is the case, for example,for adhesives based on vinylaromatic block copolymer.

Further publications such as WO 2010/141248 A1 describe systemscomprising pressure-sensitive polyisobutylene adhesives, which likewiseexhibit a low peel adhesion.

A strippable adhesive film strip having a foamed, non-pressure-sensitiveadhesive film carrier is described in WO 95/06691 A1, DE 196 49 727 A1,DE 196 49 728 A1, DE 196 49 729 A1 and DE 198 20 858 A1. Because of theintermediate carrier of foam material, a small thickness for theadhesive film strip, of below 200 μm, is not possible.

Foamed pressure-sensitive adhesive composition systems have long beenknown and are described in the prior art. In principle, polymer foamscan be produced in two ways. One way is via the effect of a blowing gas,whether added as such or resulting from a chemical reaction, and asecond way is via incorporation of hollow beads into the materialmatrix. Foams that have been produced by the latter route are referredto as syntactic foams.

Compositions foamed with hollow microbeads are notable for a definedcell structure with a homogeneous size distribution of the foam cells.With hollow microbeads, closed-cell foams without voids are obtained,the features of which include better sealing action against dust andliquid media compared to open-cell variants. Furthermore, chemically orphysically foamed materials have a greater propensity to irreversiblecollapse under pressure and temperature, and frequently show lowercohesive strength.

Particularly advantageous properties can be achieved when the microbeadsused for foaming are expandable microbeads (also referred to as“microballoons”). By virtue of their flexible, thermoplastic polymershell, foams of this kind have higher adaptation capacity than thosefilled with non-expandable, non-polymeric hollow microbeads (for examplehollow glass beads). They have better suitability for compensation formanufacturing tolerances, as is the rule, for example, in the case ofinjection-molded parts, and can also better compensate for thermalstresses because of their foam character.

Furthermore, it is possible to further influence the mechanicalproperties of the foam via the selection of the thermoplastic resin ofthe polymer shell. For example, even when the foam has a lower densitythan the matrix, it is possible to produce foams having higher cohesivestrength than with the polymer matrix alone. For instance, typical foamproperties such as adaptation capacity to rough surfaces can be combinedwith a high cohesive strength for self-adhesive foams.

EP 0 257 984 A1 discloses adhesive tapes which at least on one side havea foamed adhesive coating. Contained within this adhesive coating arepolymer beads which in turn comprise a hydrocarbon liquid and whichexpand at elevated temperatures. The scaffold polymers of theself-adhesive compositions may consist of rubbers or polyacrylates. Themicroballoons here are added either before or after the polymerization.The microballoon-containing self-adhesive compositions are processedfrom solvent and shaped to form adhesive tapes. The step of foamingtakes place logically after the coating operation. In this way,micro-rough surfaces are obtained. This results in properties such as,in particular, nondestructive redetachability and repositionability. Theeffect of the better repositionability by means of micro-rough surfacesof self-adhesive compositions foamed using microballoons is alsodescribed in other specifications such as DE 35 37 433 A1 or WO 95/31225A1.

The micro-rough surface is used in order to produce bubble-free bonding.The same use is also disclosed by EP 0 693 097 A1 and WO 98/18878 A1.Self-adhesive compositions foamed using microballoons are also knownfrom specifications U.S. Pat. No. 4,885,170 A and EP 1 102 809 B, wherethey are employed, however, as a filler for adhesive tapes for permanentbonding which are not redetachable.

Among the devices in the consumer electronics industry are electronic,optical and precision devices, in the context of this applicationespecially those devices as classified in Class 9 of the InternationalClassification of Goods and Services for the Registration of Marks (Niceclassification); 10th edition (NCL(10-2013)), to the extent that theseare electronic, optical or precision devices, and also clocks andtime-measuring devices according to Class 14 (NCL(10-2013)), such as, inparticular,

-   -   scientific, marine, measurement, photographic, film, optical,        weighing, measuring, signaling, monitoring, rescuing, and        instruction apparatus and instruments;    -   apparatus and instruments for conducting, switching, converting,        storing, regulating and monitoring electricity;    -   image recording, processing, transmission, and reproduction        devices, such as televisions and the like;    -   acoustic recording, processing, transmission, and reproduction        devices, such as broadcasting devices and the like;    -   computers, calculating instruments and data-processing devices,        mathematical devices and instruments, computer accessories,        office instruments—for example, printers, faxes, copiers,        typewriters, data-storage devices;    -   telecommunications devices and multifunction devices with a        telecommunications function, such as telephones and answering        machines;    -   chemical and physical measuring devices, control devices, and        instruments, such as battery chargers, multimeters, lamps, and        tachometers;    -   nautical devices and instruments;    -   optical devices and instruments;    -   medical devices and instruments and those for sportspeople;    -   clocks and chronometers;    -   solar cell modules, such as electrochemical dye solar cells,        organic solar cells, and thin-film cells;    -   fire-extinguishing equipment.

Technical development is going increasingly in the direction of deviceswhich are ever smaller and lighter in design, allowing them to becarried at all times by their owner, and usually being generallycarried. This is now accomplished increasingly by realization of lowweights and/or suitable size of such devices. Such devices are alsoreferred to as mobile devices or portable devices for the purposes ofthis specification. In this development trend, precision and opticaldevices are increasingly being provided (also) with electroniccomponents, thereby raising the possibilities for minimization. Onaccount of the carrying of the mobile devices, they are subject toincreased loads—in particular, to mechanical loads—as for instance byimpact on edges, by being dropped, by contact with other hard objects ina bag, or else simply by the permanent motion involved in being carriedper se. Mobile devices, however, are also subject to a greater extent toloads due to moisture exposure, temperature influences, and the like,than those “immobile” devices which are usually installed in interiorsand which move little or not at all.

The invention accordingly refers with particular preference to mobiledevices, since the adhesive used in accordance with the invention has aparticular benefit here on account of its unexpectedly good properties(very high shock resistance). Listed below are a number of portabledevices, without wishing the representatives specifically identified inthis list to impose any unnecessary restriction with regard to thesubject-matter of the invention.

-   -   Cameras, digital cameras, photography accessories (such as light        meters, flashguns, diaphragms, camera casings, lenses, etc.),        film cameras, video cameras,    -   small computers (mobile computers, handheld computers, handheld        calculators), laptops, notebooks, netbooks, ultrabooks, tablet        computers, handhelds, electronic diaries and organizers (called        “electronic organizers” or “personal digital assistants”, PDAs,        palmtops), modems,    -   computer accessories and operating units for electronic devices,        such as mice, drawing pads, graphics tablets, microphones,        loudspeakers, games consoles, gamepads, remote controls, remote        operating devices, touchpads,    -   monitors, displays, screens, touch-sensitive screens (sensor        screens, touchscreen devices), projectors,    -   reading devices for electronic books (“E-books”),    -   mini TVs, pocket TVs, devices for playing films, video players,    -   radios (including mini and pocket radios), Walkmans, Discmans,        music players for e.g. CDs, DVDs, Blu-ray, cassettes, USB, MP3,        headphones,    -   cordless telephones, mobile phones, smartphones, two-way radios,        hands-free telephones, devices for summoning people (pagers,        bleepers),    -   mobile defibrillators, blood sugar meters, blood pressure        monitors, step counters, pulse meters,    -   torches, laser pointers,    -   mobile detectors, optical magnifiers, binoculars, night vision        devices,    -   GPS devices, navigation devices, portable interface devices for        satellite communications,    -   data storage devices (USB sticks, external hard drives, memory        cards),    -   wristwatches, digital watches, pocket watches, chain watches,        stopwatches.

For these devices, a particular requirement is for adhesive tapes havinghigh holding performance that are removable easily as and when desired.

In addition, it is important that the holding performance of theadhesive tapes does not fail when the electronic device, for example acellphone, is dropped and hits the ground. The adhesive strip must thushave very high shock resistance.

It is an object of the invention to find an adhesive strip which isredetachable without residue or destruction by stretching especially inthe direction of the bond plane, which has an adhesive based onvinylaromatic block copolymers, and which exhibits particularly highshock resistance in the x,y-plane and also in the z-plane at the sametime as having reduced detachment force.

The object is achieved in accordance with the invention with apressure-sensitive adhesive strip of the generic type as recorded in themain claim. The dependent claims provide advantageous developments ofthe pressure-sensitive adhesive strip.

The invention accordingly relates to a pressure-sensitive adhesive stripwhich is redetachable without residue or destruction by extensivestretching substantially within the bond plane, comprising a layer ofadhesive, the layer of adhesive consisting of a pressure-sensitiveadhesive which is constructed on the basis of vinylaromatic blockcopolymers and tackifying resins, with selection to an extent of atleast 75% by weight (based on the total resin content) of a resin havinga DACP (diacetone alcohol cloud point) of greater than −20° C.,preferably greater than 0° C., and a softening temperature (ring & ball)of not less than 70° C., preferably not less than 100° C., and thepressure-sensitive adhesive having been foamed.

For relevantly known, strippable adhesive film strips to be redetachableeasily and without residue, they are required to possess certaintechnical bonding properties:

On stretching, the tackiness of the adhesive film strips must dropsignificantly. The lower the bonding performance in the stretched state,the less the extent to which the substrate will be damaged duringdetachment.

This property is particularly evident in adhesives based onvinylaromatic block copolymers, for which the tackiness drops to below10% in the vicinity of the yield point.

For strippable adhesive tapes to be redetachable easily and withoutresidue, they are required to have certain mechanical properties inaddition to the technical bonding properties described above.

With particular advantage, the ratio of the tensile force to thestripping force is greater than two, preferably greater than three.

The stripping force here is the force which has to be expended in orderto part an adhesive strip from a bonded joint again, by a parallelpulling in the direction of the bond plane. This stripping force is madeup of the force which is needed, as described above, to detach theadhesive tape from the bond substrates, and of the force which must beexpended in order to cause deformation of the adhesive tape. The forceneeded for deformation of the adhesive tape is dependent on thethickness of the adhesive film strip.

Within the thickness range of the adhesive film strip underconsideration (20 to 2000 μm), in contrast, the force that is needed fordetachment is independent of the thickness of the adhesive strips.

Preferably, the vinylaromatic block copolymer is at least one syntheticrubber in the form of a block copolymer having an A-B, A-B-A, (A-B)_(n),(A-B)_(n)X or (A-B-A)_(n)X structure, in which

-   -   the A blocks are independently a polymer formed by        polymerization of at least one vinylaromatic;    -   the B blocks are independently a polymer formed by        polymerization of conjugated dienes having 4 to 18 carbon atoms        and/or isobutylene, or a partly or fully hydrogenated derivative        of such a polymer;    -   X is the radical of a coupling reagent or initiator; and    -   n is an integer ≥2.

More particularly, all synthetic rubbers in the pressure-sensitiveadhesive of the invention are block copolymers having a construction asset out above. The pressure-sensitive adhesive of the invention may thusalso comprise mixtures of various block copolymers having a constructionas described above.

Suitable block copolymers (vinylaromatic block copolymers) thus compriseone or more rubber-like blocks B (soft blocks) and one or moreglass-like blocks A (hard blocks). More preferably, at least onesynthetic rubber in the pressure-sensitive adhesive of the invention isa block copolymer having an A-B, A-B-A, (A-B)₃X or (A-B)₄X construction,where the above meanings are applicable to A, B and X. Most preferably,all synthetic rubbers in the pressure-sensitive adhesive of theinvention are block copolymers having an A-B, A-B-A, (A-B)₃X or (A-B)₄Xconstruction, where the above meanings are applicable to A, B and X.More particularly, the synthetic rubber in the pressure-sensitiveadhesive of the invention is a mixture of block copolymers having anA-B, A-B-A, (A-B)₃X or (A-B)₄X structure, preferably comprising at leastdiblock copolymers A-B and/or triblock copolymers A-B-A.

Also advantageous is a mixture of diblock and triblock copolymers and(A-B)_(n) or (A-B)_(n)X block copolymers with n not less than 3.

The pressure-sensitive adhesive compositions employed are preferablythose based on block copolymers comprising polymer blocks predominantlyformed from vinylaromatics (A blocks), preferably styrene, and thosepredominantly formed by polymerization of 1,3-dienes (B blocks), forexample butadiene and isoprene or a copolymer of the two. The productsmay also contain partial or complete hydrogenation in the diene block.Block copolymers of vinylaromatics and isobutylene can likewise beutilized in accordance with the invention.

Preferably, the block copolymers of the pressure-sensitive adhesivecompositions have polystyrene end blocks.

The block copolymers that result from the A and B blocks may containidentical or different B blocks. The block copolymers may have linearA-B-A structures. It is likewise possible to use block copolymers inradial form and star-shaped and linear multiblock copolymers. Furthercomponents present may be A-B diblock copolymers. All the aforementionedpolymers can be utilized alone or in a mixture with one another.

Rather than the preferred polystyrene blocks, vinylaromatics used mayalso be polymer blocks based on other aromatic-containing homo- andcopolymers (preferably C₈ to C₁₂ aromatics) having glass transitiontemperatures of greater than 75° C., for exampleα-methylstyrene-containing aromatic blocks. In addition, it is alsopossible for identical or different A blocks to be present.

Preferably, the vinylaromatics for formation of the A block includestyrene, α-methylstyrene and/or other styrene derivatives. The A blockmay thus be in the form of a homo- or copolymer. More preferably, the Ablock is a polystyrene.

Preferred conjugated dienes as monomers for the soft block B areespecially selected from the group consisting of butadiene, isoprene,ethylbutadiene, phenylbutadiene, piperylene, pentadiene, hexadiene,ethylhexadiene and dimethylbutadiene, and any desired mixtures of thesemonomers. The B block may also be in the form of a homopolymer orcopolymer.

More preferably, the conjugated dienes as monomers for the soft block Bare selected from butadiene and isoprene. For example, the soft block Bis a polyisoprene, a polybutadiene or a partly or fully hydrogenatedderivative of one of these two polymers, such as polybutylene-butadienein particular, or a polymer formed from a mixture of butadiene andisoprene. Most preferably, the B block is a polybutadiene.

A blocks are also referred to as “hard blocks” in the context of thisinvention. B blocks are correspondingly also called “soft blocks” or“elastomer blocks”. This is reflected by the inventive selection of theblocks in accordance with their glass transition temperatures (for Ablocks at least 25° C., especially at least 50° C., and for B blocks atmost 25° C., especially at most −25° C.).

The proportion of the vinylaromatic block copolymers, styrene blockcopolymers in particular, in one preferred embodiment, in total, basedon the overall pressure-sensitive adhesive, is at least 20% by weight,preferably at least 30% by weight, further preferably at least 35% byweight.

Too low a proportion of vinylaromatic block copolymers results inrelatively low cohesion of the pressure-sensitive adhesive composition,and so the tensile strength, which is needed for stripping, is too low.

The maximum proportion of the vinylaromatic block copolymers, styreneblock copolymers in particular, in total, based on the overallpressure-sensitive adhesive composition, is at most 75% by weight,preferably at most 65% by weight, further preferably at most 55% byweight.

Too high a proportion of vinylaromatic block copolymers in turn resultsin barely any pressure-sensitive adhesion in the pressure-sensitiveadhesive composition.

Accordingly, the proportion of the vinylaromatic block copolymers,styrene block copolymers in particular, in total, based on the overallpressure-sensitive adhesive composition, is at least 20% by weight, morepreferably at least 30% by weight, further preferably at least 35% byweight, and simultaneously at most 75% by weight, more preferably atmost 65% by weight, most preferably at most 55% by weight.

Pressure-sensitive adhesive compositions (PSAs) of the invention arebased in particular on styrene block copolymers. The pressure-sensitiveadhesiveness of the polymer mixtures is achieved by addition oftackifying resins which are miscible with the elastomer phase.

Besides the at least one vinylaromatic block copolymer, the PSAs have atleast one tackifying resin in order to increase the adhesion in adesired manner. The tackifying resin ought to be compatible with theelastomer block of the block copolymers.

A “tackifying resin”, in accordance with the general understanding ofthe person skilled in the art, is understood to mean an oligomeric orpolymeric resin that increases the autohesion (tack, intrinsictackiness) of the pressure-sensitive adhesive composition compared tothe pressure-sensitive adhesive composition that does not contain anytackifying resin but is otherwise identical.

Correspondingly, a selection is made to an extent of at least 75% byweight (based on the total resin content) of a resin having a DACP(diacetone alcohol cloud point) of greater than −20° C., preferablygreater than 0° C., and a softening temperature (ring & ball) of notless than 70° C., preferably not less than 100° C.

With particular preference the tackifying resins comprise at least 75 wt% (based on the total resin content) of hydrocarbon resins or terpeneresins or a mixture of the same.

It has been found that tackifiers advantageously usable for the PSAcomposition(s) are, in particular, nonpolar hydrocarbon resins, forexample hydrogenated and non-hydrogenated polymers of dicyclopentadiene,non-hydrogenated, partly, selectively or fully hydrogenated hydrocarbonresins based on C₅-, C₅/C₉- or C₉ monomer streams, and polyterpeneresins based on α-pinene and/or ß-pinene and/or δ-limonene. Aforesaidtackifying resins can be used either alone or in a mixture. It ispossible to use either room temperature solid resins or liquid resins.Tackifying resins, in hydrogenated or non-hydrogenated form, which alsocontain oxygen may optionally be used preferably up to a maximumproportion of 25%, based on the total amount of the resins, in theadhesive composition.

The proportion of the room temperature liquid resins according to onepreferred variant is up to 15% by weight, preferably up to 10% byweight, based on the overall PSA.

The PSA of the invention contains preferably 20% to 60% by weight, basedon the total weight of the PSA, of at least one tackifying resin. Withparticular preference there is 30% to 50% by weight of tackifying resinspresent, based on the total weight of the PSA.

Further additives that can typically be utilized are:

-   -   plasticizers, for example plasticizer oils, or low molecular        weight liquid polymers, for example low molecular weight        polybutenes,    -   preferably with a proportion of 0.2% to 5% by weight, based on        the total weight of the PSA,    -   primary antioxidants, for example sterically hindered phenols,    -   preferably with a proportion of 0.2% to 1% by weight, based on        the total weight of the PSA,    -   secondary antioxidants, for example phosphites or thioethers,    -   with a proportion of 0.2% to 1% by weight, based on the total        weight of the PSA,    -   process stabilizers, for example carbon radical scavengers,    -   preferably with a proportion of 0.2% to 1% by weight, based on        the total weight of the PSA,    -   light stabilizers, for example UV absorbers or sterically        hindered amines,    -   preferably with a proportion of 0.2% to 1% by weight, based on        the total weight of the PSA,    -   processing auxiliaries,    -   preferably with a proportion of 0.2% to 1% by weight, based on        the total weight of the PSA,    -   end block reinforcer resins,    -   preferably with a proportion of 0.2% to 10% by weight, based on        the total weight of the PSA, and    -   optionally further polymers that are preferably elastomeric in        nature;    -   correspondingly utilizable elastomers include, inter alia, those        based on pure hydrocarbons, for example unsaturated polydienes        such as natural or synthetically produced polyisoprene or        polybutadiene, essentially chemically saturated elastomers, for        example saturated ethylene-propylene copolymers, α-olefin        copolymers, polyisobutylene, butyl rubber, ethylene-propylene        rubber, and chemically functionalized hydrocarbons, for example        halogenated, acrylated, allyl or vinyl ether-containing        polyolefins,    -   preferably with a proportion of 0.2% to 10% by weight, based on        the total weight of the PSA.

The nature and amount of the blend components can be selected asrequired.

It is also in accordance with the invention when the adhesivecomposition does not have some of and preferably any of the admixturesmentioned in each case.

In one embodiment of the present invention, the PSA composition alsocomprises further additives; nonlimiting examples include crystalline oramorphous oxides, hydroxides, carbonates, nitrides, halides, carbides ormixed oxide/hydroxide/halide compounds of aluminum, of silicon, ofzirconium, of titanium, of tin, of zinc, of iron or of the alkalimetals/alkaline earth metals. These are essentially aluminas, forexample aluminum oxides, boehmite, bayerite, gibbsite, diaspore and thelike. Sheet silicates are very particularly suitable, for examplebentonite, montmorillonite, hydrotalcite, hectorite, kaolinite,boehmite, mica, vermiculite or mixtures thereof. But it is also possibleto use carbon blacks or further polymorphs of carbon, for instancecarbon nanotubes.

The adhesive compositions may also be colored with dyes or pigments. Theadhesive compositions may be white, black or colored.

The plasticizers metered in may, for example, be (meth)acrylateoligomers, phthalates, cyclohexanedicarboxylic esters, water-solubleplasticizers, plasticizing resins, phosphates or polyphosphates.

The addition of silicas, advantageously of precipitated silicasurface-modified with dimethyldichlorosilane, can be utilized in orderto adjust the thermal shear strength of the PSA composition.

In a preferred embodiment of the invention, the adhesive compositionconsists solely of vinylaromatic block copolymers, tackifying resins,microballoons and optionally the abovementioned additives.

Further preferably, the adhesive composition consists of the followingcomposition:

vinylaromatic block copolymers 20% to 75% by weight tackifying resins24.6% to 60% by weight microballoons 0.2% to 10% by weight additives0.2% to 10% by weight

Further preferably, the adhesive composition consists of the followingcomposition:

vinylaromatic block copolymers 35% to 65% by weight tackifying resins34.6% to 45% by weight microballoons 0.2% to 10% by weight additives0.2% to 10% by weight

Further preferably, the adhesive composition consists of the followingcomposition:

vinylaromatic block copolymers 30% to 75% by weight tackifying resins24.8% to 60% by weight microballoons 0.2% to 10% by weight

The PSA composition of the invention has been foamed. Foaming may beeffected by means of any chemical and/or physical methods. Preferably,however, a foamed pressure-sensitive adhesive of the invention isobtained by the introduction and subsequent expansion of microballoons.

“Microballoons” are understood to mean hollow microbeads that areelastic and hence expandable in their ground state, having athermoplastic polymer shell. These beads have been filled withlow-boiling liquids or liquefied gas. Shell material employed isespecially polyacrylonitrile, PVDC, PVC or polyacrylates. Suitablelow-boiling liquids are especially hydrocarbons from the lower alkanes,for example isobutane or isopentane, that are enclosed in the polymershell under pressure as liquefied gas.

Action on the microballoons, especially by the action of heat, resultsin softening of the outer polymer shell. At the same time, the liquidblowing gas present within the shell is converted to its gaseous state.This causes irreversible extension and three-dimensional expansion ofthe microballoons. The expansion has ended when the internal andexternal pressure are balanced. Since the polymeric shell is conserved,what is achieved is thus a closed-cell foam.

A multitude of microballoon types is commercially available, whichdiffer essentially in terms of their size (6 to 45 μm diameter inunexpanded state) and the starting temperatures that they require forexpansion (75 to 220° C.). One example of commercially availablemicroballoons is the Expancel® DU products (DU=dry unexpanded) from AkzoNobel.

Unexpanded microballoon types are also available in the form of anaqueous dispersion having a solids/microballoon content of about 40% to45% by weight, and additionally also in the form of polymer-boundmicroballoons (masterbatches), for example in ethyl-vinyl acetate with amicroballoon concentration of about 65% by weight. Both the microballoondispersions and the masterbatches, like the DU products, are suitablefor production of a foamed PSA composition of the invention.

A foamed PSA composition of the invention can also be produced with whatare called pre-expanded microballoons. In the case of this group, theexpansion already takes place prior to mixing into the polymer matrix.Pre-expanded microballoons are commercially available, for example,under the Dualite® name or with the product designation Expancel xxx DE(dry expanded) from Akzo Nobel.

Preferred in accordance with the invention is for at least 90% of allcavities formed by microballoons to have a maximum diameter of 10 to 200μm, more preferably of 15 to 200 μm. The “maximum diameter” refers tothe maximum extent of a microballoon in any desired direction in space.

The diameters are determined from a cryofracture edge under the scanningelectron microscope (SEM) at 500-times magnification. The diameter ofeach individual microballoon is determined graphically.

Where foaming takes place by means of microballoons, the microballoonsmay be supplied as a batch, a paste or an unextended or extended powderto the formulation. They may also be present in suspension in solvent.

The proportion of the microballoons in the adhesive according to onepreferred embodiment of the invention is between greater than 0% and 10%by weight, more particularly between 0.25% and 5% by weight, veryparticularly between 0.5% and 1.5% by weight, based in each case on theoverall composition of the adhesive.

The figure is based on unexpanded microballoons.

A polymer composition of the invention, comprising expandable hollowmicrobeads, may additionally also contain non-expandable hollowmicrobeads. What is crucial is merely that virtually all gas-containingcaverns are closed by a permanently impervious membrane, no matterwhether this membrane consists of an elastic and thermoplasticallyextensible polymer mixture or, for instance, of elastic and—within thespectrum of the temperatures possible in plasticsprocessing—non-thermoplastic glass.

Also suitable for the PSA composition of the invention—selectedindependently of other additives—are solid polymer beads, hollow glassbeads, solid glass beads, hollow ceramic beads, solid ceramic beadsand/or solid carbon beads (“carbon microballoons”).

The absolute density of a foamed PSA composition of the invention ispreferably 350 to 990 kg/m³, more preferably 450 to 970 kg/m³, moreespecially 500 to 900 kg/m³.

The relative density describes the ratio of the density of the foamedPSA composition of the invention to the density of the unfoamed PSAcomposition of the invention having an identical formulation. Therelative density of a PSA composition of the invention is preferably0.35 to 0.99, more preferably 0.45 to 0.97, especially 0.50 to 0.90.

If the PSA of the invention has been applied to a carrier (on one orboth sides), the absolute density of the foamed PSA composition of theinvention is preferably between 220 to 990 kg/m³, more preferably 300 to900 kg/m³, more particularly 500 to 850 kg/m³. The relative density isin that case preferably between 0.20 to 0.99, more preferably between0.30 to 0.90, more particularly between 0.50 to 0.85.

Adhesive tapes produced using the polymer foam of the invention can bedesigned as

-   -   single-layer, double-sidedly self-adhesive tapes—known as        “transfer tapes”—composed of a single layer of a foamed        self-adhesive composition;    -   single-sidedly self-adhesively furnished adhesive        tapes—hereinafter “single-sided self-adhesive tapes”—in which        the layer of self-adhesive composition is a layer of the        adhesive tape of the invention;    -   double-sidedly self-adhesively furnished adhesive        tapes—hereinafter “double-sided self-adhesive tapes”—in which        one and, in particular, both layers of self-adhesive composition        of the invention is or are a layer of the adhesive tape,        examples being two-layer systems composed of a foamed        self-adhesive composition and an unfoamed self-adhesive        composition;    -   double-sidedly self-adhesively furnished adhesive tapes with a        carrier layer both sides of which bear applied adhesive        compositions, of which at least one is a composition according        to the invention.

The double-sided products here, regardless of whether they are intendedfor bonding or for sealing, may have a symmetrical or an asymmetricalconstruction.

According to one advantageous embodiment of the invention, a carrier isfurnished on both sides with one layer of adhesive composition in eachcase, with preferably the second layer of adhesive composition likewisebeing constructed on the basis of vinylaromatic block copolymers andtackifying resins.

With further preference, the first and second layers of adhesive have anidentical composition.

In one preferred embodiment of the adhesive film strip, the carrierconsists only of a single layer.

Encompassed by the concept of the invention are constructions having anextensible carrier in the middle of the adhesive strip conceivable, inwhich case the extensibility of the carrier must be sufficient to ensuredetachment of the adhesive strip by extensive stretching. Examples ofpossible carriers include highly extensible films. Examples ofextensible carriers which can be used advantageously are transparentembodiments from WO 2011/124782 A1, DE 10 2012 223 670 A1, WO2009/114683 A1, WO 2010/077541 A1, WO 2010/078396 A1.

The carrier film is produced using film-forming or extrudable polymers,which may additionally have undergone monoaxial or biaxial orientation.

In one preferred version, polyolefins are used. Preferred polyolefinsare prepared from ethylene, propylene, butylene and/or hexylene, and ineach case the pure monomers may be polymerized or else mixtures of thestated monomers may be copolymerized. Through the polymerizationtechnique and through the selection of the monomers it is possible todirect the physical and mechanical properties of the polymer film, suchas the softening temperature and/or the tensile strength, for example.

Polyurethanes, furthermore, may be used advantageously as startingmaterials for extensible carrier layers. Polyurethanes are chemicallyand/or physically crosslinked polycondensates, typically constructedfrom polyols and isocyanates. Depending on the nature of and proportionin which the individual components are used, extensible materials areobtainable which can be used advantageously in the context of thisinvention. Raw materials available to the formulator for this purposeare identified for example in EP 0 894 841 B1 and EP 1 308 492 B1. Theskilled person is aware of further raw materials from which carrierlayers of the invention can be constructed. It is advantageous,furthermore, to use rubber-based materials in carrier layers in order toproduce extensibility. As rubber or synthetic rubber or blends producedtherefrom, as starting material for extensible carrier layers, thenatural rubber may be selected fundamentally from all available gradessuch as, for example, crepe, RSS, ADS, TSR or CV products, depending onthe required levels of purity and viscosity, and the synthetic rubber orrubbers may be selected from the group of randomly copolymerizedstyrene-butadiene rubbers (SBR), butadiene rubbers (BR), syntheticpolyisoprenes (IR), butyl rubbers (IIR), halogenated butyl rubbers(XIIR), acrylate rubbers (ACM), ethylene-vinyl acetate copolymers (EVA)and polyurethanes and/or blends thereof.

Employable with particular advantage as materials for extensible carrierlayers are block copolymers. In these polymers, individual polymerblocks are linked covalently to one another. Block linkage may be in alinear form, or else in a star-shaped or graft copolymer variant. Oneexample of an advantageously employable block copolymer is a lineartriblock copolymer whose two terminal blocks have a softeningtemperature of at least 40° C., preferably at least 70° C., and whosemiddle block has a softening temperature of not more than 0° C.,preferably not more than −30° C. Higher block copolymers, such astetrablock copolymers, may likewise be employed. It is important that atleast two polymer blocks of same or different kind are present in theblock copolymer and have a softening temperature in each case of atleast 40° C., preferably at least 70° C., being separated from oneanother in the polymer chain by at least one polymer block having asoftening temperature of not more than 0° C., preferably not more than−30° C. Examples of polymer blocks are polyethers such as, for example,polyethylene glycol, polypropylene glycol or polytetrahydrofuran,polydienes, such as, for example, polybutadiene or polyisoprene,hydrogenated polydienes, such as, for example, polyethylene-butylene orpolyethylene-propylene, polyesters, such as, for example, polyethyleneterephthalate, polybutanedioladipate or polyhexanedioladipate,polycarbonate, polycaprolactone, polymer blocks of vinylaromaticmonomers, such as, for example, polystyrene or poly-[α]-methylstyrene,polyalkyl vinyl ethers, polyvinyl acetate, polymer blocks of[α],[β]-unsaturated esters such as, in particular, acrylates ormethacrylates. The skilled person is aware of corresponding softeningtemperatures. Alternatively the skilled person looks up suchtemperatures for example in the Polymer Handbook [J. Brandrup, E. H.Immergut, E. A. Grulke (Eds.), Polymer Handbook, 4th edn. 1999, Wiley,New York]. Polymer blocks may be constructed from copolymers.

In order to produce a carrier material it may also be appropriate hereto add additives and further components which enhance the film-formingproperties, which reduce the tendency for crystalline segments to formand/or which specifically improve mechanical properties or else, whereappropriate, impair such properties.

Additionally suitable are foam materials in web form (made frompolyethylene and polyurethane, for example).

The carriers may have a multi-ply design.

Furthermore, the carriers may have outer layers, barrier layers forexample, which prevent penetration of components from the adhesive intothe carrier or vice-versa. These outer layers may also have barrierproperties so as to prevent diffusion of water vapor and/or oxygenthrough the layer.

For more effective anchorage of the PSAs on the carrier, the carriersmay be pretreated by the known measures such as corona, plasma orflaming. Also possible is the use of a primer. Ideally, however, apretreatment can be omitted.

The reverse of the carrier may be subjected to an anti-adhesive physicaltreatment or coating.

Lastly, the carrier material in web form may be a material which isanti-adhesively coated on both sides, such as a release paper or arelease film, also called liner, and specifically as a temporarycarrier.

A liner (release paper, release film) is not part of an adhesive tapebut instead only an aid to the production or storage thereof or an aidto further processing by diecutting.

Furthermore, in contrast to an adhesive tape carrier, a liner is notfirmly joined to a layer of adhesive.

The thickness of the carrier layer is in the range from 10 to 200 μm,preferably between 20 and 100 μm.

The stress at 50% elongation ought to be less than 20 N/cm, preferablyless than 10 N/cm, in order to enable simple detachment withoutexcessive application of force.

Particularly advantageous is an adhesive film strip consisting of

-   -   a single-layer carrier, preferably a polyurethane, with the        carrier having an elongation at break of at least 100%,        preferably 300%, and optionally a resilience of more than 50%,        where    -   a layer of adhesive is applied to each of both sides of the        carrier, this layer being composed of the adhesive of the        invention, which is constructed on the basis of vinylaromatic        block copolymers and tackifying resins, and the composition of        the adhesives being more preferably identical.

The production and processing of the PSAs may take place either fromsolution or from the melt. Application of the PSAs to the carrier layermay take place by direct coating or by lamination, more particularly hotlamination.

Typical processed forms of the pressure-sensitive adhesive strips of theinvention are adhesive tape rolls and also adhesive strips of the kindobtained, for example, in the form of diecuts.

All of the layers preferably have the form, essentially, of a cuboid.With further preference all the layers are joined to one another overtheir full area.

Optionally there may be a non-adhesive grip tab region provided,starting from which the detachment operation can be performed.

The general expression “adhesive tape” for the purposes of thisinvention encompasses all sheetlike structures such as two-dimensionallyextended films or film sections, tapes with extended length and limitedwidth, tape sections, diecuts, labels, and the like.

The (single-layer) adhesive film strip preferably has a thickness of 20μm to 2000 μm, more preferably of 30 to 1000 μm, with particularpreference 50 to 60 μm or 100 μm or 150 μm or 300 μm

In a preferred embodiment of the pressure-sensitive adhesive strip, thecarrier has a thickness of between 20 and 60 μm, preferably 50 μm, andthe identical layers of adhesive on the carrier likewise each have athickness of between 20 and 60 μm, preferably 50 μm.

Particular preference is given here to two embodiments, the first having25 μm of adhesive on either side of a 50 μm carrier, and the secondhaving 35 μm of adhesive on either side of a 30 μm carrier.

With reference to the figures and examples described hereinafter,particularly advantageous embodiments of the invention will beelucidated in detail, without any intention thereby to subject theinvention to unnecessary restriction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a three-layer pressure-sensitive adhesive strip of theinvention;

FIG. 2 shows a three-layer pressure-sensitive adhesive strip of theinvention in an alternative embodiment;

FIG. 3 shows a one-layer pressure-sensitive adhesive strip of theinvention;

FIG. 4 the process with one mixing unit, wherein the microballoons areadded directly in the first mixing unit;

FIG. 5 the process with two mixing units, wherein the microballoons areadded in the first mixing unit;

FIG. 6 the process with two mixing units, wherein the microballoons areadded only in the second mixing unit;

FIG. 7 shows a lateral section through a specimen according to example5; and

FIG. 8 shows a lateral section through a specimen according to example8.

FIG. 1 shows the pressure-sensitive adhesive strip of the inventioncomposed of three layers 1, 2, 3, which is redetachable without residueor destruction by extensive stretching substantially within the bondplane.

The strip consists of a carrier 1, the carrier 1 being of one-layerembodiment.

On the carrier there are external inventive adhesive layers 2, 3 oneither side.

The protruding end of the carrier 1 may serve as a grip tab, but is notmandatorily present.

In FIG. 2, the pressure-sensitive adhesive strip of the invention isshown in a variant. The strip consists of three layers 1, 2, 3 which arearranged congruently one above another.

In order to produce a grip tab for pulling, to achieve the extensivestretching particularly in the bond plane, one end of the adhesive filmstrip is made non-adhesive on both sides, by the application ofpreferably siliconized pieces of film or of paper 4.

FIG. 3 shows a single-layer pressure-sensitive adhesive strip 5 whichhas a grip tab composed of siliconized film or paper pieces 4 applied toboth sides of the adhesive strip 5.

Furthermore, the invention encompasses a method for producing anadhesive of the invention which comprises expanded microballoons—seeFIG. 4—wherein

-   -   the constituents for forming the adhesive such as polymers,        resins or fillers and unexpanded microballoons are mixed in a        first mixing unit and heated to expansion temperature under        elevated pressure,    -   the microballoons are expanded on exit from the mixing unit,    -   the adhesive composition mixture along with the expanded        microballoons is formed into a layer in a roll applicator,    -   the adhesive composition mixture along with the expanded        microballoons is optionally applied to a carrier or release        material in web form.

Furthermore, the invention encompasses a method for producing anadhesive of the invention which comprises expanded microballoons—seeFIG. 5—wherein

-   -   the constituents for forming the adhesive such as polymers,        resins or fillers and unexpanded microballoons are mixed in a        first mixing unit under elevated pressure and are heated to a        temperature below the expansion temperature of the        microballoons,    -   the mixed, more particularly homogeneous adhesive is transferred        from the first mixing unit into a second unit and is heated to        expansion temperature under elevated temperature,    -   the microballoons are expanded in the second unit or on exit        from the second unit,    -   the adhesive composition mixture along with the expanded        microballoons is formed into a layer in a roll applicator,    -   the adhesive composition mixture along with the expanded        microballoons is optionally applied to a carrier or release        material in web form.

Furthermore, the invention encompasses a method for producing anadhesive of the invention which comprises expanded microballoons—seeFIG. 6—wherein

-   -   the constituents for forming the adhesive such as polymers,        resins or fillers are mixed in a first mixing unit,    -   the mixed, more particularly homogeneous adhesive is transferred        from the first mixing unit into a second mixing unit, which is        supplied simultaneously with the unexpanded microballoons,    -   the microballoons are expanded in the second mixing unit or on        exit from the second mixing unit,    -   the adhesive composition mixture along with the expanded        microballoons is formed into a layer in a roll applicator,    -   the adhesive composition mixture along with the expanded        microballoons is optionally applied to a carrier or release        material in web form.

According to one preferred embodiment of the invention, the adhesive isshaped in a roll applicator and applied to the carrier material.

There is generally no need to degas compositions foamed microballoonsprior to coating in order to obtain a homogeneous, continuous coating.The expanded microballoons displace the air incorporated into theadhesive composition during compounding. In the case of highthroughputs, it is nevertheless advisable to degas the compositionsprior to coating in order to obtain a homogeneous feed of composition inthe roll gap. The degassing is ideally effected directly upstream of theroll applicator at mixing temperature and with a pressure differentialfrom ambient pressure of at least 200 mbar.

In addition, it is advantageous when

-   -   the first mixing unit is a continuous unit, especially a        planetary roller extruder, a twin-screw extruder or a pin        extruder,    -   the first mixing unit is a batchwise unit, especially a Z        kneader or an internal mixer,    -   the second mixing unit is a planetary roll extruder, a        single-screw or twin-screw extruder or a pin extruder and/or    -   the shaping unit in which the adhesive composition along with        the expanded microballoons is shaped to give a carrier layer is        a calender, a roll applicator or a gap formed by a roll and a        fixed doctor.

With the processes of the invention, solvent-free processing of allpreviously known components of adhesive compositions and those describedin the literature, especially self-adhesive compositions, is possible.

The above-described processes within the concept of the invention invariants of particularly excellent configuration are illustratedhereinafter, without any intention to impose unnecessary restrictionthrough the choice of the figures depicted.

FIG. 4 shows a particularly advantageously configured process forproducing a foamed pressure-sensitive self-adhesive tape.

In a continuous mixing unit, for example a planetary roller extruder(PRE), a (self-) adhesive composition is produced.

For this purpose, the reactants E that are to form the adhesivecomposition are introduced into the planetary roller extruder PRE 10. Atthe same time, the unexpanded microballoons MB are incorporatedhomogeneously under elevated pressure into the self-adhesive compositionduring the compounding process.

The temperatures required for homogeneous production of theself-adhesive composition and for expansion of the microballoons areadjusted with respect to one another such that the microballoons foam upin the self-adhesive composition M on exit from the PRE 10 as a resultof the pressure drop on exit from the die, and in so doing break throughthe surface of the composition.

With a roll applicator 30 as shaping unit, this foam-like adhesivecomposition M is calendered and coated onto a carrier material in webform, for example release paper TP; in some cases, further foaming canstill take place in the roll gap. The roll applicator 30 consists of adoctor roll 31 and a coating roll 32. The release paper TP is guidedonto the latter via a pick-up roll 33, such that the release paper TPtakes up the adhesive composition K from the coating roll 32.

At the same time, the expanded microballoons MB are forced back into thepolymer matrix of the adhesive composition K, and hence a smooth surfaceis generated.

FIG. 5 shows a further particularly advantageously configured processfor producing a foamed pressure-sensitive self-adhesive tape.

The planetary roller extruder PRE 10 has two successive mixing zones 11,12 in which a central spindle rotates. In addition, there are sixplanetary spindles per heating zone. Further reactants are added to theinjection ring 13, for example plasticizer or liquid resin. An exampleof a suitable apparatus is the planetary roller extruder from Entex inBochum.

Subsequently, the microballoons are incorporated under elevated pressurehomogeneously into the self-adhesive composition in a second mixingunit, for example a single-screw extruder, heated above the expansiontemperature and foamed on exit.

For this purpose, the adhesive composition K formed from the reactants Eis introduced here into the single-screw extruder SSE 20; at the sametime, the microballoons MB are introduced. The single-screw extruder SSE20 has a total of four heating zones over its run length 21.

An example of a suitable apparatus is a single-screw extruder fromKiener.

During the expansion caused by the pressure drop at the die exit of SSE20, the microballoons MB break through the surface of the composition.

With a roll applicator 30, this foam-like adhesive composition M iscalendered and coated onto a carrier material in web form, for examplerelease paper TP; in some cases, further foaming can still take place inthe roll gap. The roll applicator 30 consists of a doctor roll 31 and acoating roll 32. The release paper TP is guided onto the latter via apick-up roll 33, such that the release paper TP takes up the adhesivecomposition K from the coating roll 32.

At the same time, the expanded microballoons MB are forced back into thepolymer matrix of the adhesive composition K, and hence a smooth surfaceis generated.

FIG. 6 shows a further particularly advantageously configured processfor producing a foamed pressure-sensitive self-adhesive tape.

In a continuous mixing unit, for example a planetary roller extruder(PRE), a (self-) adhesive composition is produced.

Here, the reactants E that are to form the adhesive composition areintroduced into the planetary roller extruder PRE 10. The planetaryroller extruder PRE 10 has two successive mixing zones 11, 12 in which acentral spindle rotates. In addition, there are six (6) planetaryspindles per heating zone.

Further reactants are added to the injection ring 13, for exampleplasticizer or liquid resin.

An example of a suitable apparatus is the planetary roller extruder fromEntex in Bochum.

Subsequently, the microballoons are incorporated homogeneously underelevated pressure into the self-adhesive composition in a second mixingunit, for example a single-screw extruder, heated above the expansiontemperature and foamed on exit.

For this purpose, the adhesive composition K formed from the reactants Eis introduced here into the single-screw extruder SSE 20; at the sametime, the microballoons MB are introduced. The single-screw extruder SSEhas a total of four heating zones over its run length 21.

An example of a suitable apparatus is a single-screw extruder fromKiener.

During the expansion caused by the pressure drop at the die exit of SSE20, the microballoons MB break through the surface of the composition.

With a roll applicator 30, this foam-like adhesive composition M iscalendered and coated onto a carrier material in web form, for examplerelease paper TP; in some cases, further foaming can still take place inthe roll gap. The roll applicator 30 consists of a doctor roll 31 and acoating roll 32. The release paper TP is guided onto the latter via apick-up roll 33, such that the release paper TP takes up the adhesivecomposition K from the coating roll 32.

At the same time, the expanded microballoons MB are forced back into thepolymer matrix of the adhesive composition K, and hence a smooth surfaceis generated.

With falling gap pressure in the roll gap, there is a decrease in thebonding areas of the coated foamed self-adhesive compositions, since themicroballoons are then forced back to a lesser degree, as can beinferred from FIG. 4. FIG. 4 shows the bonding areas as a function ofthe coating process or parameter. The gap pressure required is highlydependent on the composition system used; the higher the viscosity, thegreater the gap pressure should be, depending on the layer thicknessdesired and the coating speed chosen. In practice, a gap pressure ofgreater than 4 N/mm has been found to be useful; with exceptionally highcoating speeds greater than 50 m/min, with low applications ofcomposition (basis weights less than 70 g/m²) and high-viscositycompositions (50 000 Pa*s at 0.1 rad and 110° C.), gap pressures greaterthan 50 N/mm may even be required.

It has been found to be useful to adjust the temperature of the rolls tothe expansion temperature of the microballoons. Ideally, the rolltemperature of the first rolls is above the expansion temperature of themicroballoons in order to enable further foaming of the microballoonswithout destroying them. The last roll should have a temperature equalto or below the expansion temperature in order that the microballoonshell can solidify and the smooth surface of the invention forms.

Many units for continuous production and processing of solvent-freepolymer systems are known. Usually, screw machines such as single-screwand twin-screw extruders of different processing lengths and withdifferent equipment are used. Alternatively, continuous kneaders of awide variety of different designs, for example including combinations ofkneaders and screw machines, or else planetary roller extruders, areused for this task.

Planetary roller extruders have been known for some time and were firstused in the processing of thermoplastics, for example PVC, where theywere used mainly for charging of the downstream units, for examplecalenders or roll systems. Their advantage of high surface renewal formaterial and heat exchange, with which the energy introduced viafriction can be removed rapidly and effectively, and of short residencetime and narrow residence time spectrum, has allowed their field of useto be broadened recently, inter alia, to embrace compounding processesthat require a mode of operation with exceptional temperature control.

Planetary roller extruders exist in various designs and sizes accordingto the manufacturer. According to the desired throughput, the diametersof the roller cylinders are typically between 70 mm and 400 mm.

Planetary roller extruders generally have a filling section and acompounding section.

The filling section consists of a conveying screw, into which all solidcomponents are metered continuously. The conveying screw then transfersthe material to the compounding section. The region of the fillingsection with the screw is preferably cooled in order to avoid caking ofmaterial on the screw. But there are also embodiments without a screwsection, in which the material is applied directly between central andplanetary spindles. However, this is of no significance for the efficacyof the process of the invention.

The compounding section consists of a driven central spindle and severalplanetary spindles that rotate around the central spindle within one ormore roll cylinders having internal helical gearing. The speed of thecentral spindle and hence the peripheral velocity of the planetaryspindles can be varied and is thus an important parameter for control ofthe compounding process.

The materials are circulated between the central and planetary spindles,i.e. between planetary spindles and the helical gearing of the rollsection, such that the materials can be dispersed under the influence ofshear energy and external temperature control to give a homogeneouscompound.

The number of planetary spindles that rotate in each roll cylinder canbe varied and hence adapted to the demands of the process. The number ofspindles affects the free volume within the planetary roller extruderand the residence time of the material in the process, and additionallydetermines the size of the area for heat and material exchange. Thenumber of planetary spindles affects the compounding outcome via theshear energy introduced. Given a constant roller cylinder diameter, itis possible with a greater number of spindles to achieve betterhomogenization and dispersion performance, or a greater productthroughput.

The maximum number of planetary spindles that can be installed betweenthe central spindle and roller cylinder is dependent on the diameter ofthe roller cylinder and on the diameter of the planetary spindles used.In the case of use of greater roller diameters as necessary forachievement of throughputs on the production scale, or smaller diametersfor the planetary spindles, the roller cylinders can be equipped with agreater number of planetary spindles. Typically, up to seven planetaryspindles are used in the case of a roller diameter of D=70 mm, while tenplanetary spindles, for example, can be used in the case of a rollerdiameter of D=200 mm, and 24, for example, in the case of a rollerdiameter of D=400 mm.

It is proposed in accordance with the invention that the coating of thefoamed adhesive compositions be conducted in a solvent-free manner witha multiroll applicator system.

These may be applicator systems consisting of at least two rolls with atleast one roll gap up to five rolls with three roll gaps.

Also conceivable are coating systems such as calenders (I,F,Lcalenders), such that the foamed adhesive composition is shaped to thedesired thickness as it passes through one or more roll gaps.

It has been found to be particularly advantageous to choose thetemperature regime for the individual rolls such that controlled furtherfoaming can take place if appropriate, in such a way that transferringrolls can have a temperature above or equal to the foaming temperatureof the microballoon type chosen, whereas receiving rolls should have atemperature below or equal to the foaming temperature in order toprevent uncontrolled foaming and where all rolls can be set individuallyto temperatures of 30 to 220° C.

In order to improve the transfer characteristics of the shapedcomposition layer from one roll to another, it is also possible to useanti-adhesively finished rolls or patterned rolls. In order to produce asufficiently precisely shaped adhesive film, the peripheral speeds ofthe rolls may have differences.

The preferred 4-roll applicator is formed by a metering roll, a doctorroll, which determines the thickness of the layer on the carriermaterial and is arranged parallel to the metering roll, and a transferroll disposed beneath the metering roll. At the lay-on roll, whichtogether with the transfer roll forms a second roll gap, the compositionand the material in web form are brought together.

Depending on the nature of the carrier material in web form which is tobe coated, coating can be effected in a co-rotational orcounter-rotational process.

The shaping system may also be formed by a gap formed between a roll anda fixed doctor. The fixed doctor may be a knife-type doctor or else astationary (half-)roll.

In an alternative process for producing an adhesive composition, allconstituents of said composition are dissolved in a solvent mixture(benzine/toluene/acetone). The microballoons are converted to a slurryin benzine and stirred into the dissolved adhesive composition. As soonas the microballoons are distributed homogeneously in the solution, theadhesive composition can be coated; for example, the coating can beaccomplished by means of a doctor blade onto a conventional PET liner.

In the first step, the coated adhesive is dried exposed at 100° C. for15 min. After the drying, the adhesive layer is covered with a secondply of PET liner and foamed in the oven at 150° C. for 5 min,specifically covered between two liners, in order to produce aparticularly smooth surface.

The surface thus produced has a roughness R_(a) of less than 15 μm, morepreferably less than 10 μm.

The surface roughness is preferably R_(a) is a unit for the industrialstandard for the quality of the final surface processing and constitutesthe average height of the roughness, especially the average absolutedistance from the center line of the roughness profile within the rangeof evaluation. R_(a) is measured by means of laser triangulation.

The expansion temperature is usually always higher than the dryingtemperature.

FIGS. 7 and 8 show an adhesive composition of the invention in lateralsection.

As a result of the foaming of the adhesive composition, technicalbonding and performance properties are improved.

This reduction in the drop in peel adhesion is promoted by the highsurface quality, produced as a result of the pressing of the expandedmicroballoons back into the polymer matrix during the coating operation.

Furthermore, relative to the unfoamed composition with the same polymerbasis, the foamed self-adhesive composition gains additional performancefeatures such as, for example, an improved impact resistance at lowtemperatures, boosted peel adhesion on rough substrates, greater dampingand/or sealing properties, or conformance of the foam adhesive to unevensubstrates, a more favorable crushing/hardness behavior, and enhancedcompression capacity.

Further elucidation of the characteristic properties and additionalfunctions of the self-adhesive compositions of the invention isaccomplished in part in the examples.

The invention is elucidated in more detail below by means of a number ofexamples.

In these examples, the constituents of the PSAs were dissolved at 40% inbenzine/toluene/acetone, admixed with a benzine slurry of themicroballoons, and coated out in the desired film thickness, using acoating bar, onto a PET film equipped with a silicone release, followedby evaporation of the solvent at 100° C. for 15 min so as to dry thelayer of composition.

After drying, the adhesive layer was lined with a second ply of PETliner, free from any air inclusions, and was foamed in an oven betweenthe two liners at 150° C. for 5 min. By foaming between two liners,products are obtainable that have particularly smooth surfaces. All ofthe examples given feature an RA value of less than 15 μm.

Pressure-sensitive adhesive strips with the desired dimensions wereobtained by diecutting.

EXAMPLES Examples 1 to 3

Comparative example Example 1 Example 2 Example 3 Fraction FractionFraction Fraction Raw material (wt %) (wt %) (wt %) (wt %) KRATON 110250 48.6 48.1 47.40 Dercolyte A115 45 46.4 46.0 45.5 Wingtack 10 4.5 3.02.9 2.9 Aging inhibitor 0.5 0.5 0.5 0.5 Expancel 920 DU20 0 1.5 2.5 3.5Total 100.00 100.0 100.0 100.0

Constituents of the adhesive:

KRATON styrene-butadiene-styrene block copolymer from Kraton 1102polymers, 83 wt % 3-block, 17 wt % 2-block; block polystyrene content:30 wt % Dercolyte A solid α-pinene tackifying resin having a ring andball 115 softening temperature of 115° C. and a DACP of 35° C. Wingtack10 liquid hydrocarbon resin from Cray Valley Expancel 920 microballoonsDU20

Aging inhibitors used include Irganox 1010 (phenolic antioxidant).

Com- parative Exam- Exam- example Example 1 ple 2 ple 3 Thickness [μm]109 107 103 109    Density [g/cm³] 1 0.752 0.593  0.50 Microballoon [wt%] 1.5 2.5 3.5 Peel adhesion, [N/cm] 9 10.0 8.5 8.0 steel Peel adhesion,PE [N/cm] 7 6.9 6.7 6.2 Ball drop, (13.8 g) [cm] 50 225 >245 Ball drop,(32.6 g) [cm] — 125 185*   Transverse impact [mJ] 364 656 542 420   toughness Elongation at [%] 975 about 1000 836 631    break Detachmentforce [N/cm] 3 2.4 2.2

Examples 1 to 3 show the effect exerted by an increasing amount ofmicroballoons in the adhesive, as compared with an unfoamed adhesive ofequal thickness.

Result:

-   -   Shock exposure in the z-plane increases with increasing        microballoon content (ball drop)    -   Shock exposure in the x,y-plane increases with increasing        content of microballoons, with a maximum observable at a        microballoon content of 1.5 wt % (transverse impact toughness)    -   The detachment force falls with increasing microballoon content,        in spite of increasing shock robustness

Examples 4 to 7

Compar- ative example 2 Example 4 Example 5 Example 6 Example 7 FractionFraction Fraction Fraction Fraction Raw material (wt %) (wt %) (wt %)(wt %) (wt %) KRATON 50 49.1 48.8 48.6 48.3 1102 Dercolyte 44 46.2 45.945.7 45.5 A115 Wingtack 10 4.5 3.0 3.0 3.0 3.0 Aging 1.5 1.2 1.3 1.2 1.2inhibitor Expancel 0 0.5 1 1.5 2 920 DU20 Total 100.00 100.0 100.0 100.0100.0

Microballoon content Density Ball weight Height E (wt %) (kg/m³) (g)(cm) (J) Comparative 0 1000 32.6 25 0.9005 example Example 4 0.5 88432.6 85 1.1124 Example 5 1 799 32.6 165 1.2272 Example 6 1.5 698 32.6250 1.2714 Example 7 2 624 110 85 1.0948

Stripping force Microballoon Density F average F max content (wt %)(kg/m³) (N/cm) (N/cm) Comparative 0 1000 2.17 2.52 example Example 4 0.5884 2.08 2.31 Example 5 1 799 1.94 2.10 Example 6 1.5 698 2.04 2.19Example 7 2 624 1.39 1.98

Examples 4 to 7 show the influence exerted by an increasing microballooncontent in the adhesive, by comparison with an unfoamed adhesive.

Result:

-   -   Even at a microballoon content of 0.5 wt % there is a distinct        improvement measurable in the shock robustness (ball drop)    -   Shock robustness increases with increasing microballoon content    -   Stripping force falls with increasing microballoon content

Examples 8 to 9

In examples 8 and 9, three-layer specimens were compared with oneanother.

Comparative example 2 consists of a 50 μm PU film as intermediatecarrier, to which on both sides an unfoamed adhesive is applied, withthe composition indicated, in each case with a coat weight of 25 g/m²and a layer thickness of 25 μm on either side.

Example 8 consists of a 50 μm PU film as intermediate carrier, to whichon both sides an unfoamed adhesive of the composition specified isapplied, in each case with a coat weight thickness of 20 g/m² and alayer thickness of 20 μm on either side. The specimen, lined on eitherside with PET liner, was foamed in an oven at 150° C. for 5 min to atotal thickness of 100 μm.

Example 9 consists of a 30 μm PU film as intermediate carrier, to whichon both sides an unfoamed adhesive of the composition specified isapplied, in each case with a coat weight thickness of 28 g/m² and alayer thickness of 28 μm on either side. The specimen, lined on eitherside with PET liner, was foamed in an oven at 150° C. for 5 min to atotal thickness of 100 μm.

Comparative example 2 Examples 8 and 9 Raw material Fraction (wt %)Fraction (wt %) KRATON 1102 50 48.6 Dercolyte A115 44 45.7 Wingtack 104.5 3.0 Aging inhibitor 1.5 1.2 Expancel 920 DU20 0 1.5 Total 100.00100.0

Comparative example 2 Example 8 Example 9 Ball drop [cm] 13.8 g 45 245245 Ball drop [mJ] 13.8 g 60.92 331.68 331.68 Ball drop [cm] 32.6 g —145 145 Ball drop [mJ] 32.6 g — 463.72 463.72 Push out [N/cm²] 32 24 31Transverse impact toughness 270 469 [mJ] PA steel [N/cm] 7 5 6.8 PA PE[N/cm] 5 4.2 4.9 Stripping force [N/cm] 7 6 4.9 Tears [#] 180° 0 0 0Tears [#] 90° 3 0 0

Examples 8 and 9 show the effect which foamed adhesives have on the peelangle of the adhesive strip.

Result:

-   -   A foamed three-layer construction still displays high shock        robustness and no tears at 180° and 90° peel angles    -   At a 90° peel angle, a foamed three-layer construction is more        tear-resistant than an unfoamed three-layer construction of        equal thickness

Test Methods

Unless otherwise indicated, all of the measurements were conducted at23° C. and 50% relative humidity.

The mechanical and technical adhesive data were determined as follows:

Resilience/Elasticity

To measure the resilience, the pressure-sensitive adhesive strips wereextended by 100%, kept at this extension for 30 s and then released.After a wait time of 1 min, the length was measured again.

The resilience is then calculated as follows:R=((L ₁₀₀ −L _(end))/L ₀)*100with R=resilience in %L₁₀₀: Length of the adhesive strip after extension by 100%L₀: Length of the adhesive strip prior to extensionL_(end): Length of the adhesive strip after relaxation for 1 min.

The resilience corresponds here to the elasticity.

Elongation at Break, Tensile Strength and Strain at 50% Elongation

The elongation at break, the tensile strength and the strain at 50%elongation were measured in accordance with DIN 53504 using dumbbellspecimens of size S3 at a separation speed of 300 mm per minute. Thetest conditions were 23° C. and 50% rel. air humidity.

Detachment Force

The detachment force (stripping force or stripping strain) wasdetermined by means of a film of adhesive with dimensions of 50 mmlength×20 mm width having a non-adhesive grip tab region at the top end.The film of adhesive was adhered between two steel plates, arrangedcongruently to one another and with dimensions of 50 mm×30 mm, using anapplied pressure of 50 newtons in each case. At their lower end, thesteel plates each have a drilled hole for accommodating an S-shapedsteel hook. The lower end of the steel hook carries a further steelplate, via which the test arrangement can be fixed, for measurement, inthe lower clamping jaw of a tensile testing machine. The adhesive bondsare stored at +40° C. for a time of 24 hours. After reconditioning toroom temperature, the adhesive film strip is pulled apart with a pullingspeed of 1000 mm per minute, parallel to the bond plane and withoutcontact with the edge regions of the two steel plates. During thisprocedure, the required detachment force in newtons (N) is measured. Thefigure reported is the average of the stripping strain values (in N permm²), measured in the range in which the adhesive strip underwentdetachment from the steel substrates over a bonding length of between 10mm and 40 mm.

Tearing Test

Strips 10 mm wide and 40 mm long are produced by punching from theadhesive tape under investigation. These strips are adhered over alength of 30 mm to a PC plate conditioned with ethanol, thus leaving agrip tab 10 mm long. A second PC plate is adhered to the second side ofthe bonded strips, in such a way that the two PC plates lie flush oneabove the other. The assembly is rolled down 10 times (five times backand forth) using a 4 kg roller. After a take time of 24 h, the stripsare stripped from the bonded joint by the grip tab, manually, at

-   -   a) a 90° angle and    -   b) a 180° angle.

An evaluation is made of how many specimens can be redetached withoutresidue.

Tackifying Resin Softening Temperature

The tackifying resin softening temperature is conducted by the relevantmethodology, known as ring & ball and standardized in ASTM E28.

DACP

The DACP is the diacetone cloud point and is determined by cooling aheated solution of 5 g of resin, 5 g of xylene and 5 g of diacetonealcohol to the point at which the solution turns cloudy.

Falling Ball Test (Impact Toughness, Ball Drop)

A square sample with a frame shape was cut from the adhesive tape underinvestigation (external dimensions 33 mm×33 mm; border width 3.0 mm;internal dimensions (window cutout) 27 mm×27 mm). This sample wasadhered to an ABS frame (external dimensions 50 mm×50 mm; border width12.5 mm; internal dimensions (window cutout) 25 mm×25 mm; thickness 3mm). On the other side of the double-sided adhesive tape, a PMMA windowmeasuring 35 mm×35 mm was adhered. The bonding of ABS frame, adhesivetape frame and PMMA window took place in such a way that the geometriccenters and the diagonals lay in each case one above another (corner tocorner). The bond area was 360 mm². The bond was pressed under 10 barfor 5 s and stored for 24 hours with conditioning at 23° C./50% relativehumidity.

Immediately after storage, the bonded assembly of ABS frame, adhesivetape and PMMA window was placed, with the protruding edges of the ABSframe, on a frame rack (sample holder) in such a way that the assemblywas aligned horizontally and the PMMA window pointed downward in freesuspension. A steel ball of the weight indicated in each case wasdropped centrally onto the PMMA window of the sample thus arranged, thedrop being vertical from a height of 250 cm (through the window of theABS frame) (measuring conditions 23° C., 50% relative humidity). Witheach sample, three investigations were carried out, unless the PMMAwindow had already detached.

The falling ball test is passed if the bond has not parted in any of thethree investigations.

In order to be able to compare experiments with different ball weights,the energy was calculated as follows:E=height [m]*ball weight [kg]*9.81 kg/m*s²

Push-Out Strength (z-Plane)

The push-out test provides information about the level of resistance ofan adhesive bond of a component in a frame-shaped body, such as a windowin a housing.

A rectangular, frame-shaped sample was cut out of the adhesive tapeunder investigation (external dimensions 43 mm×33 mm; border width 2.0mm in each case, internal dimensions (window cutout) 39 mm×29 mm, bondarea on top and bottom sides 288 mm² in each case). This sample wasadhered to a rectangular ABS polymer frame(ABS=acrylonitrile-butadiene-styrene copolymers) (external dimensions 50mm×40 mm, border width of the long borders 8 mm in each case; borderwidth of the short borders 10 mm in each case; internal dimensions(window cutout) 30 mm×24 mm; thickness 3 mm). Adhered to the other sideof the sample of the double-sided adhesive tape was a rectangular PMMAsheet (PMMA=polymethyl methacrylate) with dimensions of 45 mm×35 mm. Thefull bond area of the adhesive tape available was utilized. The ABSframe, adhesive tape sample and PMMA window were bonded in such a waythat the geometric centers, the bisecting lines of the acute diagonalangles and the bisecting lines of the obtuse diagonal angles of therectangles each lay on top of one another (corner on corner, long sideson long sides, short sides on short sides). The bond area was 360 mm².The bond was pressed under 10 bar for 5 s and stored with conditioningat 23° C./50% relative humidity for 24 hours.

Immediately after storage, the adhesive assembly composed of ABS frame,adhesive tape and PMMA sheet was placed with the protruding edges of theABS frame onto a frame rack (sample holder) in such a way that theassembly was oriented horizontally and the PMMA sheet pointed downwardsin free suspension.

A plunger is then moved perpendicularly from above through the window ofthe ABS frame at a constant speed of 10 mm/s, such that it pressescentrally onto the PMMA plate, and the respective force (determined fromrespective pressure and contact area between plunger and plate) isrecorded as a function of the time between first contact of the plungerwith the PMMA plate up to shortly after the PMMA plate has dropped off(measuring conditions 23° C., 50% relative humidity). The force actingimmediately before failure of the adhesive bond between PMMA plate andABS frame (maximum force F_(max) in the force-time diagram, in N) isrecorded as the outcome of the push-out test.

Transverse Impact Toughness; x,y-Plane

A square sample with a frame shape was cut from the adhesive tape underinvestigation (external dimensions 33 mm×33 mm; border width 3.0 mm;internal dimensions (window cutout) 27 mm×27 mm). This sample wasadhered to an ABS frame (external dimensions 45 mm×45 mm; border width10 mm; internal dimensions (window cutout) 25 mm×25 mm; thickness 3 mm).On the other side of the double-sided adhesive tape, a PMMA windowmeasuring 35 mm×35 mm was adhered. The bonding of ABS frame, adhesivetape frame and PMMA window took place in such a way that the geometriccenters and the diagonals lay in each case one above another (corner tocorner). The bond area was 360 mm². The bond was pressed under 10 barfor 5 s and stored for 24 hours with conditioning at 23° C./50% relativehumidity.

Immediately after storage, the bonded assembly of ABS frame, adhesivetape and PMMA window with the protruding edges of the ABS frame wasclamped into a sample holder in such a way that the assembly wasoriented vertically. The sample holder was subsequently insertedcentrally into the intended holder of the DuPont impact tester. Theimpact head, weighing 300 g, was inserted such that the rectangularstriking geometry with dimensions of 20 mm×3 mm was central and flushagainst the upwardly directed end-face side of the PMMA window.

A weight with a mass of 150 g, guided on two guide rods, was droppedvertically from a height of 3 cm onto the assembly thus arranged ofsample holder, sample and impact head (measuring conditions 23° C., 50%relative humidity). The height of the falling weight was raised in stepsof 3 cm until the impact energy introduced caused destruction of thesample as a result of the transverse impact load, and the PMMA windowparted from the ABS frame.

In order to be able to compare experiments with different samples, theenergy was calculated as follows:E[J]=height [m]*mass weight [kg]*9.81 kg/m*s²

For each product, five samples were tested, and the average energy valuewas reported as a characteristic number for the transverse impacttoughness.

Peel Adhesion

The determination of the peel adhesion (in accordance with AFERA 5001)is carried out as follows. The defined adhesion substrate used isgalvanized steel plate with a thickness of 2 mm (acquired from RochollGmbH) or a polyethylene block, respectively. The bondable sheetlikeelement under investigation is cut to a width of 20 mm and a length ofabout 25 cm, provided with a handling section and immediately thereafterpressed down five times using a 4 kg steel roller, at a rate of advanceof 10 m/min, onto the particular adhesion substrate selected. Directlyfollowing that, the bondable sheetlike element is peeled from thesubstrate at an angle of 180° and a speed v=300 mm/min, using a tensiletesting instrument (from Zwick), and the force required to achieve thisat room temperature is recorded. The measurement value (in N/cm) is theaverage value resulting from three individual measurements.

Static Glass Transition Temperature Tg

Glass transition points—referred to synonymously as glass transitiontemperatures—are reported as the result of measurements by means ofdifferential scanning calorimetry (DSC) according to DIN 53 765,especially sections 7.1 and 8.1, but with uniform heating and coolingrates of 10 K/min in all heating and cooling steps (cf. DIN 53 765;section 7.1; note 1). The sample weight is 20 mg.

The invention claimed is:
 1. A pressure-sensitive adhesive strip that isredetachable without residue or destruction by extensive stretchingsubstantially within the bond plane, the pressure-sensitive adhesivestrip comprising a layer of adhesive consisting of a pressure-sensitiveadhesive having a composition comprising one or more vinylaromatic blockcopolymers at 20% to 75% by weight of the total composition, one or moretackifying resins at 24.6% to 60% by weight of the total composition,and microballoons at 0.2% to 10% by weight of the total composition,wherein at least 75% by weight (based on the total resin content) of theone or more tackifying resins is at least one resin having a DACP(diacetone alcohol cloud point) of greater than −20° C., and a softeningtemperature (ring & ball) of not less than 70° C., and thepressure-sensitive adhesive having been foamed, wherein the foamedpressure-sensitive adhesive comprises a surface having a surfaceroughness R_(a) of less than 15 μm and the surface roughness R_(a)constitutes an average height of the roughness along the surface of thefoamed pressure-sensitive adhesive.
 2. The pressure-sensitive adhesivestrip according to claim 1, wherein the one or more vinylaromatic blockcopolymers comprise polymer blocks predominantly formed fromvinylaromatics (A blocks), and blocks predominantly formed bypolymerization of 1,3-dienes (B blocks).
 3. The pressure-sensitiveadhesive strip according to claim 2, wherein the vinylaromatics forconstruction of the A blocks comprise styrene, polystyrene, α-methylstyrene and/or other styrene derivatives.
 4. The pressure-sensitiveadhesive strip according to claim 2, wherein a monomer for the B blocksis selected from the group consisting of butadiene, isoprene,ethylbutadiene, phenylbutadiene, piperylene, pentadiene, hexadiene,ethylhexadiene and dimethylbutadiene, and mixtures of said monomers. 5.The pressure-sensitive adhesive strip according to claim 1, wherein theone or more vinylaromatic block copolymers used are at least onesynthetic rubber in the form of a block copolymer having an A-B, A-B-A,(A-B)_(n), (A-B)_(n)X or (A-B-A)_(n)X structure, in which: the A blocksare independently a first polymer formed by polymerization of at leastone vinylaromatic; the B blocks are independently a second polymerformed by polymerization of conjugated dienes having 4 to 18 carbonatoms and/or isobutylene, or a partly or fully hydrogenated derivativeof the second polymer; X is the radical of a coupling reagent orinitiator; and n is an integer ≥2.
 6. The pressure-sensitive adhesivestrip according to claim 1, wherein the one or more tackifying resinscomprises at least 75% by weight hydrocarbon resins or terpene resins,or a mixture thereof.
 7. The pressure-sensitive adhesive strip accordingto claim 1, wherein the pressure-sensitive adhesive consists of thefollowing composition: the one or more vinylaromatic block 35% to 65% byweight copolymers the one or more tackifying resins 34.6% to 45% byweight the microballoons 0.2% to 10% by weight additives 0.2% to 10% byweight.


8. The pressure-sensitive adhesive strip according to claim 1, whereinan absolute density of the foamed pressure-sensitive adhesive is 350 to990 kg/m³, and/or a relative density is 0.35 to 0.99, wherein therelative density is a ratio of a density of the foamedpressure-sensitive adhesive to a density of the unfoamedpressure-sensitive adhesive.
 9. The pressure-sensitive adhesive stripaccording to claim 1, wherein, when the pressure-sensitive adhesive hasbeen applied to one or both sides of a carrier, an absolute density ofthe foamed pressure-sensitive adhesive is between 220 to 990 kg/m³,and/or a relative density is between 0.20 to 0.99, wherein the relativedensity is a ratio of a density of the foamed pressure-sensitiveadhesive to a density of the unfoamed pressure-sensitive adhesive. 10.The pressure-sensitive adhesive strip according to claim 9, wherein thecarrier is 10 to 200 μm thick.
 11. The pressure-sensitive adhesive stripaccording to claim 9, wherein the carrier has an elongation at break ofat least 100%, and optionally a resilience of more than 50%.
 12. Thepressure-sensitive adhesive strip according to claim 1, wherein thepressure-sensitive adhesive strip has a carrier to one side of which thepressure-sensitive adhesive is applied as a layer, or to both sides ofwhich the pressure-sensitive adhesive is applied as a layer, and furtherwherein the carrier, optionally, has a thickness of between 20 and 60μm, and the layer of the pressure-sensitive adhesive, optionally, has athickness of between 20 and 60 μm.
 13. The pressure-sensitive adhesivestrip according to claim 1, wherein the pressure-sensitive adhesivestrip is of single-layer implementation, with the thickness of thepressure-sensitive adhesive strip being from 20 μm to 2000 μm.
 14. Thepressure-sensitive adhesive strip according to claim 1, wherein thesurface roughness Ra is less than 10 μm.
 15. A method comprising:bonding components with the pressure-sensitive adhesive strip accordingto claim 1.